This invention relates generally to a measurement and control system utilizing optical attenuation to detect movement of a system to which it is attached. More specifically, the invention relates to an optical attenuation system and components thereof which will generate signals proportional to the movement of an article to which the system is attached. As an example, movement of a human hand may be detected so as to provide an interaction device which will generate signals proportional to hand and finger movements for control of a multi-degree-of-freedom robotic hand or the like.
Optical measurement systems are known and have been utilized in a wide variety of applications. Optical systems have been utilized particularly in the telecommunications industry, wherein an optical fiber is utilized as a communications link with a light signal being modulated to represent information which can then be detected and demodulated at the opposite end of the fiber for use. Optical systems have the unique ability to be introduced into hostile environments, particularly those having strong electromagnetic or electrostatic interference which may affect wiring, addressing, and signal processing aspects of a sensing, measuring or processing system. The optical system will not be adversely affected by such interference which may generate significant electric noise levels in electrical systems. In general, an optical system will include a source of light which may be introduced into an optical fiber and subsequently carried to a light sensor for converting the light signal into an electrical signal for use. The optical fibers utilized in such a system comprise a transparent core of suitable glass or plastic material which is carried within a relatively thin cylindrical cladding wherein the cladding has an index of refraction which is less than the refractive index of the core material. When a light signal is introduced into the optical fiber, the core material functions as a wave guide and will transmit or propagate the light signal with relatively small transmission losses, thereby enabling its effective use. The fiber optic cable will function reliably without undue attenuation of the light signals even if gradual turns or bends are introduced into the fiber.
It has been found in the prior art that relatively short bends in an optical fiber may significantly attenuate the light signals transmitted therethrough to enable use of an optical fiber in various measurement systems. Fiber optic systems have been developed for measuring mechanical motion or remote force measurements by introducing relatively short bends or what has been labeled the microbend effect inherent in fiber optic cables. The microbends introduced into a fiber optic cable result in the attenuation of the propagated light signal by scattering a portion of the signal from the fiber core to the cladding and/or to the surrounding environment.
Optical fiber microbending has been utilized to detract a portion of the light signal from a fiber optic cable or to input additional light signals into the fiber without damaging the fiber. One such system is shown in U.S. Pat. No. 4,253,727 showing a microbend coupler utilizing this phenomena. Alternatively, other uses for the concept of optical fiber micro bending are known. The technique may be utilized to measure displacement or force which would result in deformation of an optical fiber causing further attenuation which could be quantified to yield these measurements. One example of an optical sensor to monitor vibration or mechanical motion of equipment to which the sensor is attached is shown in U.S. Pat. No. 4,408,495. This phenomenon has also been utilized to determine the forces acting along a structure such as an oil or gas pipeline as shown in U.S. Pat. No. 4,477,725.
In these examples, the attenuation of the transmitted optical signal is determinative of the physical variable to be measured and must be of high sensitivity and include relatively complex signal processing means to measure fine variations in these variables. On the other hand, other optical systems may be responsive to alternative optical characteristics such as phase or polarization angle of the light source being transmitted through the fiber optic cable. A deformation sensor which may utilize other optical characteristics is shown in U.S. Pat. No. 4,420,251. It is recognized in such a system that the incident optical energy must be polarized by means of additional structure thereby adding complexity to the system.
Optical systems have also been utilized in other measurement systems such as an optical fiber based spectrometer utilized to determine the presence or absence of elements or the like in a sample or process being analyzed. The spectrometer measures the spectral radiance of light signals carried over a plurality of optical fibers at a distance from the sample being analyzed to avoid unwanted interference with measuring and processing apparatus. The spectrometer includes an optical attenuator which includes a plurality of eccentrically located apertures, the positions of which are variable. By suitably positioning the apertures on a fixed plane perpendicular to the emitted light rays, the desired amount of attenuation of light input from the optical fibers may be controlled by the misalignment of the optical fiber ends.
In yet another system as shown in U.S. Pat. No. 4,733,068, a fiber optic sensor array is utilized to form a tactile sensor utilized in manipulation activities for intelligent machines and robotics. The tactile sensor as described in this patent utilizes an array of transmitting and detecting optical fibers optically coupled to one another and sandwiched between a pliable spacer arrangement. As the supporting structure is deformed by an external force, the amount of light coupled into the detecting fiber from the transmitting fiber will vary according to the deformation. The changes in the received signals can then by processed to yield an indication of the deformation and thus the amount of force applied to the supporting structure. Control signals may be developed from this system and utilized as feedback so as to give an indication of the force at a remote location which may be especially useful in robotic applications.
It can thus be seen that optical systems have been utilized increasingly for various functions and provide an effective and accurate means by which physical variables may be measured. More recently, there has been found a need for interactive devices to facilitate communication between a user and a remote device such as an intelligent machine or robot. As robots become more of a integral portion of society, there is an increasing need for an effective interface between the user and the robot for control and manipulation of the robotic controls. For example, there have been developed electronic sensors which will register the head position and orientation of a user's head. Signals are developed to be interfaced with a remote robot to manipulate a robots camera eyes or the like in the same direction. Similarly, other interactive devices have been developed to interface with and control robotic functions such as a DataGlove developed by VPL Research, Inc., which translates hand and finger movements into electrical signals to control a remote robot. Such an interaction device enables the precision, control and agility of the human hand to be translated into robotic movements and manipulations enabling extremely effective control thereover. The DataGlove utilizes fiber optic cables sandwiched between two layers of cloth and formed into a glove which can be worn on the users hand. The fiber optic cables are run the length of each finger and thumb and doubled back upon themselves to be anchored at both ends to an interface board located in the base of the glove. Each fiber optic cable includes a light-emitting diode at one end and a phototransistor at the other.
In this system, the fiber optic cables are treated such that light will escape upon flexion movements of the hand of the user. Treating the fiber optic cables in this manner results in attenuation of the transmitted light signals. Alternatively, the treatment may also cause fatigue, deformation and eventual breakage. The phototransistor of the system will convert the light signals which it receives into electrical signals which can subsequently be input to a processing and control apparatus which will control the robotic movements. It should be recognized that the generation of signals proportional to the relatively complex movements of the human hand would enable complex maneuvers and manipulations of robotic apparatus to be carried out in both an easy and effective manner. It should also be recognized that such as system could be incorporated to include and take advantage of other human motions. This system requires complicated processing circuitry and is very costly to manufacture. Treating of the fiber optic cables may also result in reduced ability to form a repeatable and reliable system.
The translation of movements of the human hand have also been accomplished by a mechanical linkage device known as the Sarcose Hand Master developed by the A. D. Little Company. In this assembly, a mechanical linkage is associated with each finger and thumb on a human hand and includes electronic motion sensors which will transmit finger and thumb position information to be processed and utilized by a control system. The system may transduce up to sixteen joint angular positions and may also measure flexion and abduction or adduction. The electronic motion sensors require precise calibration as well as relatively complex processing or transformation and storage of the developed signals. It should be recognized that any mechanical design will inherently include limitations based upon the user and is somewhat cumbersome. Similarly, a mechanical design is subject to limited life and imprecise tuning and repetition of the system.